The present invention generally pertains to a method and an apparatus for multi-cavity injection molding of plastic products and is particularly directed to a highly efficient and highly controllable method and an apparatus for core-back injection molding of multi-component plastic products. Core-back injection molding makes possible the injection of a first plastic material into a mold cavity, followed by retracting a barrier means, in order to enable injection of a second plastic material without separating any mold halves.
Heretofore core-back multi-cavity injection molding of multi-component plastic products were made by simultaneous injection of all cavities by a first plastic material and subsequently in time by simultaneous injection of all cavities by a second plastic material.
Examples of prior art core-back injection molding may be seen in the following U.S. Pat. Nos.: 4,157,883 to Mares; 4,508,676 to Sorensen; 4,726,758 to Sekine et al. and 4,840,760 to Oishi.
The problem with such injection molding is that it is very inefficient because only one injection unit is operating at the time, and it is not very controlled because all the cavities are filled at the same time, causing slow injection speeds and balancing problems in filling the individual cavities evenly.
The present invention enables very efficient injection molding because both injection units may be operated at the time, and the present invention enables very controlled injection because it is possible to inject only one half of the cavities by a specific injection unit at the same time, or even only one quarter of the cavities by a specific injection unit at the same time.